To provide a sterilizer and a sterilizing method which effectively sterilize a large amount of liquid without applying a high frequency pulse electric field.

The sterilizer includes a guide member 2 having a flow passage 3 through which liquid food material flows, a plurality of electrodes 21 for applying an electric field to a liquid flowing through the guide member 2, and a cooling medium pipe 22 which cools the liquid food material flowing through the flow passage 3 by means of a cooling medium flowing through the cooling medium pipe.